Relation of concavity in the expiratory flow-volume loop to dynamic hyperinflation during exercise in COPD
Introduction
Exercise intolerance is one of the major symptoms contributing to declining quality of life in patients with COPD. The pathogenesis is multifactorial. One of the main contributors is reduced ventilatory capacity caused by expiratory airflow limitation (O'Donnell, 2006, O'Donnell et al., 2001, Porszasz et al., 2005).
COPD patients may experience airflow limitation both at rest and during exercise (Hyatt, 1961). Flow limitation occurs once airflow reaches a speed at which the flow is independent from pleural pressure, however, in emphysema the negative pressure dependence occurs at all lung volumes (Ingram and Schilder, 1966a, Ingram and Schilder, 1966b). Flow limitation can exacerbate breathing effort, leading to high intrathoracic pressure (Hyatt, 1961, Milic-Emili, 2000). Concomitantly, as ventilation increases during exercise and expiratory time decreases, expiratory airflow limitation makes it impossible to complete a full expiration to the relaxation volume. This yields increases in end-expiratory lung volume (EELV), a phenomenon known as dynamic hyperinflation (Casaburi and Porszasz, 2006, O'Donnell, 2006, O'Donnell et al., 2001, O'Donnell and Webb, 1993, Vogiatzis et al., 2004). As dynamic hyperinflation proceeds, end inspiratory volumes approach the total lung capacity where lower lung compliance yields higher inspiratory work and, eventually, inspiratory muscle fatigue and exercise-limiting dyspnea (Eltayara et al., 1996, O'Donnell and Webb, 1993).
O’Donnell et al. have provided confirmatory evidence correlating Borg dyspnea ratings and measurements of inspiratory capacity (IC) to dynamic hyperinflation and a decrease in endurance time during submaximal constant work rate cycle exercise. Their findings were highly reproducible and responsive to interventions reducing dynamic hyperinflation in severe COPD (O'Donnell et al., 1998).
We have previously reported a computerized technique enabling breath-by-breath analysis of the shape of the expiratory limb of the flow-volume loop (Ma et al., 2006, Ma et al., 2010). We intended to test the hypothesis that the observed rapid decrease in expiratory flow during spontaneous breathing during exercise correlates well with dynamic hyperinflation and determine whether this measure concavity of the expiratory limb of the spontaneous flow-volume loop signals imminent exercise termination in severe COPD patients. We also compared the differences in physiologic responses in groups with and without expiratory flow-volume loop concavity.
Section snippets
Study subjects
Seventeen patients (11 males) with severe to very severe COPD (FEV1: 38 ± 10%pred), and 12 healthy subjects (5 males) gave written informed consent for their participation in this study. The study was approved by the Los Angeles Biomedical Research Institute Institutional Review Board; all subjects were studied at this institution. Inclusion criteria for the COPD patients was a baseline post-bronchodilator FEV1 less than 60% predicted of normal by European Coal and Steel Standards (Quanjer et
Results
The demographic characteristics and resting spirometric function of the subjects are presented in Table 1. Among the COPD subjects, we noted two distinct patterns of configuration of the expiratory limb of the spontaneous flow-volume loop. At end-exercise, in 12 subjects severe concavity of the EFVL was seen (RAR = 0.40 ± 0.03, group HCONC), whereas in 5 subjects mild or no concavity (RAR = 0.52 ± 0.04, group LCONC) was present at end-exercise (Table 2); a dividing criterion of RAR = 0.47 at end-
Discussion
Concavity of the expiratory limb of the flow-volume loop is a marker of expiratory flow limitation. In this study, for the first time, we have shown that concavity of the expiratory limb of the spontaneous flow-volume loop is closely correlated with dynamic hyperinflation during exercise measured by serial inspiratory capacity maneuvers. Both dynamic hyperinflation and expiratory flow limitation are markers of ventilatory limitation. Determination of concavity of expiratory limb of the
References (31)
- et al.
Inspiratory capacity and decrease in lung hyperinflation with albuterol in COPD
CHEST J.
(2002) - et al.
Emerging concepts in the evaluation of ventilatory limitation during exercise: the exercise tidal flow-volume loop
Chest
(1999) - et al.
Graphic analysis of flow-volume curves: a pilot study
BMC Pulm. Med.
(2016) - et al.
Breath-by-breath quantification of progressive airflow limitation during exercise in COPD: a new method
Respir. Med.
(2010) Expiratory flow limitation: Roger S. Mitchell lecture
Chest
(2000)- et al.
Exercise training decreases ventilatory requirements and exercise-induced hyperinflation at submaximal intensities in patients with COPD
Chest
(2005) Psychophysical bases of perceived exertion
Med. Sci. Sports Exerc.
(1982)A comparison of the maximum voluntary ventilation with the forced expiratory volume in one second: an assessment of subject cooperation
J. Occup. Med.
(1982)- et al.
Reduction of hyperinflation by pharmacologic and other interventions
Proc. Am. Thorac. Soc.
(2006) - et al.
Mechanics of air flow in airway obstruction
Annu. Rev. Med.
(1973)
Test of wave-speed theory of flow limitation in elastic tubes
J. Appl. Physiol.
Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease
Am. J. Respir. Crit. Care Med.
Characteristics of chord time constant and F-V curve configuration in testing small airway functions for smokers
Hua Xi Yi Ke Da Xue Xue Bao
Tangent time constant and wave-speed mechanism of F–V curve configuration in smokers and clinical significance
Hua Xi Yi Ke Da Xue Xue Bao
The interrelationships of pressure, flow, and volume during various respiratory maneuvers in normal and emphysematous subjects
Am. Rev. Respir. Dis.
Cited by (34)
Corrected formula for rectangular area ratio (RAR), a parameter used to quantify airflow limitation on expiratory flow-volume curves
2022, Respiratory MedicineCitation Excerpt :As noted above, the RAR calculation presented by Ma et al. [2] would erroneously underestimate the true RAR and could potentially label more patients to have an obstructive defect compared to what would be truly observable. This has important implications for the results reported in their original paper as well as several other papers that have utilized the same formula without modification [2–5]. The correct formula, as presented here, should be used to update the results and determine if the results remain consistent.
Area under flow-volume loop may predict severe exacerbation in COPD patients with high grade of dyspnea
2021, Respiratory Physiology and NeurobiologyCitation Excerpt :However, FEV1/FVC is insensitive to determine early obstructive small airway pathology, because FVC declines first with initial preservation of FEV1/FVC [30]. Instead, curvilinearity of FVL was found to be a simple indicator of airflow limitation, even in patients with normal values of FEV1 and FEV1/FVC [31,32]. The novel spirometric parameter ‘AreaFE%’ which reflects the curvilinearity of FVL provides greater sensitivity in showing early disease [33].
Ventilation during exercise: Practical aspects on the analysis of cardiopulmonary exercise testing
2024, Zeitschrift fur Pneumologie